What is simulated
The model reproduces the two-microphone transfer-function configuration of ISO 10534-2 (the same configuration as ASTM E1050). A plane wave travels down the tube, reflects from your sample, and the reflection is evaluated across frequency. The sample geometry is resolved directly, including the visco-thermal losses in its narrow pores and channels, so no fitted material parameters such as flow resistivity or tortuosity are needed for designs supplied as CAD.
From the complex reflection coefficient R(f) we report:
Tube diameters and frequency range
As in a physical tube, the usable band depends on the tube diameter: only plane waves may propagate, which sets an upper limit of roughly f < 0.58 c/d for a circular tube. We offer the two common configurations:
- Ø29 mm: about 500–6300 Hz.
- Ø100 mm: about 50–1600 Hz.
- Both, stitched: one curve from about 50 Hz upward.
Accepted files and required inputs
- Geometry: STL, STEP, IGES, 3MF, OBJ, or a ZIP of these. Up to 95 MB per file and 10 files per request.
- Either the full sample as it would sit in the tube, or one periodic unit cell plus the sample thickness and diameter.
- Units of the CAD file (for example millimetres), so the geometry is scaled correctly.
- Backing condition: rigid backing, or the depth of any air gap behind the sample.
- Tube diameter and frequency range: Ø29 mm (about 500–6300 Hz), Ø100 mm (about 50–1600 Hz), or both stitched into one curve.
- Whether you also need transmission loss.
Deliverables
- Normal-incidence sound absorption coefficient α(f).
- Normalised surface impedance Zs(f), real and imaginary parts.
- Complex reflection coefficient R(f).
- CSV data, plots, and a short PDF report describing the method, mesh convergence and validation reference.
Turnaround
We check your files within one business day. After payment, results are delivered within 72 hours, or within 24 hours with the priority option.
Pricing
- $50 per sample for samples 1 to 9, and $40 per sample from the tenth onward. For example, 10 samples cost $490.
- Add-ons: transmission loss +$20 per sample; full band (both tube diameters) +$15 per sample; results within 24 h +50%.
- Custom design studies, such as optimisation for a target band, are quoted per project.
- You pay by PayPal (card accepted) only after we confirm your files can be simulated. Prices in USD, excluding any applicable taxes.
Normal incidence, not random incidence
The impedance tube, physical or numerical, gives absorption for sound arriving straight on to the sample. Product data sheets often quote random-incidence absorption measured in a reverberation room (ISO 354), which generally differs from normal-incidence values. The two should not be used interchangeably.
Simulation, not accredited testing. Results are a numerical simulation of the standard test configuration, not an accredited laboratory measurement. If you need a certified test report for product certification or building-code compliance, use the simulation to choose the design and then have the final design measured by an accredited laboratory.